Norfair is leet, just gotta watch out for CP characters since it's not a good stage for ROB against most characters. The same could be said of Brinstar.
Banning Japes is for suckers, it's the only stage with a really high ceiling and the water/hazard is borderline at best.
Delfino vs DDD? Me no likey walk-offs and walls
Eh, they're easy enough to avoid. I feel the advantage of the rest of the stage is more than worth the risk, you just have to be a little more careful around those parts. The arrangement of the platforms (very high, some of them hanging over the ledges) is helpful during the flying portions, where you spend the most time, and ROB can eat him on the water parts.
As far as Halberd is concerned, the ceiling isn't that much lower than normal. The platform is a ***** and you're not going to hang out there anyway, so it's like a 5% difference at worst. :/ Like fighting anyone else, you want to avoid exposing ROB's blind spot and Dedede will attack it with his fat penguin head with impunity from beneath if you give him the chance. But... Dedede is slower than ROB, just go for the sides and he just isn't fast enough to capitalize. Play it like FD and it's just like that, except you trade ~5% of survivability for an uneven floor and the ability to attack him from beneath half the time.
I tried JJ but... Camping the side platforms just seems to put him at the perfect height for BAir spam ROB can't do much about, low enough to poke at your feet and stay beneath most attacks himself. So... what am I doing wrong here?
He's so gigantic the upper central platform isn't even that safe. The sides are short so the opportunity to rack up damage on his otherwise predictable recovery rarely appears. All the ledges are nice and the high ceiling probably hurts more than it helps but I guess I just don't see it. *shrug*